The present invention relates to a power management method, and in particular, to a system and method for performing power management automatically without software protocols.
Regulation of power consumption is an important concern in computer systems, particularly in mobile computers using a battery as a power supply. The Advanced Configuration and Power Interface (ACPI) standard is implemented in computer systems for managing power consumption, the architecture thereof is shown in FIG. 1a. 
ACPI is implemented through cooperation of hardware and software. According to the design, power management is accomplished by delivering commands from the operating system to the hardware through drivers and the system management bus (SMBUS), and power consumption is reduced by decreasing the operating voltage and frequency accordingly. FIG. 1a shows a conventional system architecture comprising a software layer 101, a hardware layer 103 and an ACPI layer 112 therebetween. The operating system 104 in software layer 101 comprises an Operating System Power Management (OSPM) API, labeled 106 in the figure. The OSPM 106 is executed to assess utilization of an application 102, and regulate power consumption accordingly. Thus a corresponding power management command is delivered to the ACPI layer 112 through device drivers 108 and ACPI driver 110 and is transmitted to the hardware layer 103 through SMBUS.
The ACPI layer 112 architecture comprising programs, control tables and ACPI registers resides between the hardware and software layers. In hardware layer 103, the power management command is received by the South Bridge 124, and is transferred to voltage controller 122 and frequency controller 126 through System Management Bus (SMBUS) 128 to control voltages and frequencies. Based on the power management command, the voltage controller 122 can adjust operating voltages of Central Processing Unit (CPU) 114, Accelerated Graphics Port (AGP) 116 and memory 120, and the frequency controller 126 generates corresponding operating frequencies for each of the system components.
When hardware performance is decreased to reduce power consumption, however, the software driven power management efficiency is compromised and reliability suffers as the software is reliant on hardware for execution. For example, when CPU 114 enters state C3, data in CPU 114 is lost, data in the cache loses consistency, and the system is unable to handle master requests and interrupt requests. A considerable number of clock cycles are required to recover from the state C3, thus the software power management system is unable to reflect hardware utilization in real-time, thus reducing power consumption efficiency.